Expansion joint structure for concrete slabs

ABSTRACT

The invention relates to an expansion joint structure ( 1 ) to be placed between adjacent concrete slabs ( 66   a   ,66   b ) in a concrete slab system. The structure comprises a first profile element ( 10 ) to be attached to an edge of a first concrete slab, and a second profile element ( 12 ) to be attached to an edge of a second concrete slab, said profile elements being joined together by removable connecting trips ( 28 ) such that there is a gap ( 26 ) between the profile elements. In an expansion joint structure according to the invention the profile elements and connecting strips constitute a single continuous entity of extruded aluminium profile. The connecting strips are attached by their edges to the profile elements through very thin necks that keep the elements together during the pouring of the slab. An expansion joint structure according to the invention is positioned on the concreting base at the correct height prior to the pouring of the concrete slabs. During the pouring, the connecting strips block the gap between the profile elements and keep it clean. When the concrete has hardened enough, the connecting strips are thorn off and the resulting gap is filled with elastic sealant. The first profile element of the expansion joint structure is designed such that it serves as a construction joint form so that concrete slabs on the different sides of the expansion joint can be poured at different times, if necessary.

[0001] The invention relates to an expansion joint reinforcing structurefor concrete slabs, comprising a first profile element to be attached toan edge of a first concrete slab, and a second profile element to beattached to an edge of a second, adjacent, concrete slab, said profileelements being joined together by at least one removable connectingstrip such that there is a gap between the profile elements.

[0002] A widely used flooring structure in construction engineering is aconcrete slab on grade, poured either direct on top of leveled soil oron top of a thermal insulator layer placed on the ground. Shrinkage ofthe concrete as well as thermal contraction and expansion tend to causecracking in large slabs, whereby large slabs have to be divided intosmaller sub-slabs by means of expansion or isolation joints.Deformations caused by shrinkage and thermal expansion and contractionwill thus occur at the expansion joints and the slabs will otherwiseremain crackless.

[0003] The simplest way of making expansion joints is to first pour awhole concrete slab and then, as setting has begun, divide it intosmaller sections separated by grooves saw-cut on the surface of the slabby means of a diamond-blade saw. Subsequent contraction cracks will thenappear at the grooves. The edges of saw-cut expansion joints are proneto crumbling and chipping, so they are totally unsuitable for heavilyloaded floors. From the prior art we also know of expansion jointstructures embedded in concrete with metal reinforcements at the edgesof the expansion joints. One such structure is disclosed in the patentdocument FI 952994. The reinforcing joint structure is embedded in freshconcrete, and the joint between the flat steel bars is saw-cut open oncethe concrete has hardened. The joint is then filled with elasticmaterial. The installation of such an expansion joint structure istedious, because the joint structure has to be pushed intoalready-leveled fresh concrete. Moreover, saw-cutting the expansionjoint means extra work.

[0004] Reference documents GB 1139538, U.S. Pat. No. 3,068,763, U.S.Pat. No. 3,276,335, and U.S. Pat. No. 3,455,215 disclose expansion jointstructures embedded in the surface of a concrete slab. These structuresare weak and not intended to be anchored in the concreting base.Therefore, they cannot serve as construction joint forms or screedguides during the floating of the concrete slab. In most such solutions,the gap between the two halves of the joint structure is closed using aflexible sealing agent attached to the joint structure and remainingpartly within the cast. Such a flexible and soft sealing agent wears andbreaks easily so that the joint begins to leak. Moreover, the sealingagent within the cast cannot be replaced.

[0005] Patent document FI 982675 discloses an expansion joint structurewith a sheetmetal profile and metallic angle profile loosely attached tothe sheetmetal profile by rivets or flexible bolts, for example. Thesheetmetal profile simultaneously serves as a form for the slab to becast. The sheetmetal profile and angle profile both have protrudingbondage means through which they become attached to the concrete. Thejoint structure is placed such that it rests on corrugated steel rodsdriven into the concreting base at correct locations and heights, or onconcrete legs cast on the concreting base, after which the slab ispoured. As the concrete shrinks, the angle profile comes off thesheetmetal profile, thereby opening an expansion joint between theprofiles.

[0006] A drawback of this solution is the poor functionality of theexpansion joint. An expansion joint caused solely by the shrinkage ofconcrete is so narrow that it cannot be sealed with a sealing agent.This means that the expansion joint will not be watertight. In order toachieve a sufficient joint width the gap between the sheetmetal profileand angle profile has to be enlarged with the result that the gap willbe filled with concrete when the concrete is poured. Therefore, prior tosealant installation, the gap has to be thoroughly cleaned with e.g. agrinder, adding to the building costs. In spite of the cleaning,concrete dust and crumbles often remain in the gap, affecting theadhesion of the sealant to the walls of the gap. It is thereforedifficult to male the expansion joint watertight. Moreover, it issomewhat difficult to anchor the expansion joint structure to theconcreting base and set it at the correct height.

[0007] An object of the invention is to provide a new expansion jointstructure which reduces the drawbacks and disadvantages associated withexpansion joints according to the prior art.

[0008] An expansion joint structure according to the invention ischaracterized in that which is specified in the independent claim. Someadvantageous embodiments of the invention are specified in the dependentclaims.

[0009] An expansion joint structure according to the invention is areinforcing structure designed to be placed between individual slabs ofa concrete slab system, comprising a first profile element to beattached to an edge of a first concrete slab, and a second profileelement to be attached to an edge of a second, adjacent, concrete slab.The profile elements are joined together by removable connecting stripssuch that there is a clear gap between the profile elements. In anexpansion joint structure according to the invention the profileelements and connecting strips constitute a single continuous entity ofextruded aluminum profile. The connecting strips are attached by theiredges to the profile elements through very thin necks that keep theelements together during the casting of the slab. When the concrete hashardened enough, the connecting strips are torn off whereby the thinnecks will break and the connection between the profile elementsdisappears. An expansion joint structure according to the invention ispositioned on the concreting base at the correct height prior to thecasting of the concrete slabs. As the concrete sets, the joint structureremains within the slab system and becomes part of the cast. Duringcasting, the connecting strips block the gap between the profileelements and keep it clean. When the concrete has hardened enough, theconnecting strips are torn off whereby the profile elements will becomedisconnected. The resulting gap is filled with elastic sealant,completing the expansion joint.

[0010] An advantage of the invention is that the expansion joint can becompleted quicker. Saw-cutting and cleaning the joints, which tasks arerequired in expansion joint construction techniques according to theprior art, are no longer required when using the structure according tothe invention, resulting in savings in construction costs.

[0011] Another advantage of the invention is that it enhances thequality of expansion joints. Using the structure according to theinvention, the gap between the profile elements is clean, smooth-edged,and wide enough so that an elastic sealant can be easily installed inthe gap and, moreover, the adhesion between the sealant and gap walls isgood. This way, the expansion joint will be watertight, adding to thedurability and life of the joint.

[0012] A further advantage of the invention is that it makes themaintenance of the expansion joint easier. The sealant in the wide gapbetween the profile elements can be easily repaired or replaced, ifnecessary, should the sealant come off the walls of the gap or otherwiselose its watertightness.

[0013] Yet another advantage of the invention is that it has severalfunctions. An expansion joint structure supported on the concreting baseat a correct installation height serves as a screed mark during thecasting of the concrete and, furthermore, it can also serve as aconstruction joint form.

[0014] A still further advantage of the invention is that it is simplein construction, cheap to manufacture and well suited to industrialproduction.

[0015] The invention will be now described in detail. Reference is madeto the accompanying drawings in which

[0016]FIG. 1 is a diagonal front view of an expansion joint structureaccording to the invention,

[0017]FIG. 2 is a cross-section view of an expansion joint of a freshlycast concrete slab with an expansion joint structure according to theinvention, and

[0018]FIG. 3 is a cross-section view of an expansion joint of a hardenedconcrete slab with an expansion joint structure according to theinvention.

[0019]FIG. 1 shows, by way of example, a diagonal front view of anexpansion joint structure 1 according to the invention. The expansionjoint structure is depicted in vertical position, i.e. in the positionin which it will be installed. The expansion joint structure comprisestwo parallel metal profiles: a first profile element 10 and a secondprofile element 12. The first profile element is a metal profile havinga cross sectional shape which resembles a so-called trapezoid,comprising three substantially parallel planar portions: upper portion16, lower portion 18, and middle portion 20. The upper and lowerportions are in substantially the same vertical plane, but the middleportion is clearly in a different plane than the upper and lowerportions. The middle portion is connected to the upper and lowerportions through slanted flange portions 22 such that the portionstogether constitute a single metal profile. On one surface of eachflange portion there is a short bonding projections 24 to increase thebonding of the first profile element to the concrete.

[0020] The second profile element 12 is an L-shaped metal profileattached parallel to the upper portion 16 of the first profile elementby means of two removable connecting strips 28 in the longitudinaldirection of the profile elements. The attachment is realized such thata first flank of the second profile element stands upright parallel tothe upper portion of the first profile element, and a second flank ofthe second profile element lies horizontally, projecting away from thefirst profile element. The connecting strips are metallic stripsattached by their first edges to the first profile element and by theirsecond edges to the second profile element. Between the first flank ofthe second profile element 12 and the upper portion 16 of the firstprofile element 10 there is a gap 26 the width of which can be set asdesired at the manufacturing stage of the expansion joint structure.Advantageously the width of the gap is about 10 mm. On the first flankof the second profile element there is a longitudinal ledge 30 and,conversely, on the upper portion 16 of the first profile element thereis a corresponding ledge 32 such that the two ledges face each other inthe gap 26.

[0021] The first and second profile elements are interconnected by afirst connecting strip 28 at the upper edge of the gap 26, and by asecond connecting strip at the middle of the gap where the ledges 30 and32 are located. At the upper portion of the gap 26, in the longitudinaldirection of the expansion joint structure, there is thus formed aclosed cavity confined by the profile elements 10, 12 and connectingstrips 28. At the lower portion of the gap there is formed a channel 40confined by the profile elements and lower connecting strip such thatthe downward-facing side of the channel is open. Advantageously thechannel is square-shaped and has a width of about 12 mm. Additionally,there is, in the longitudinal direction of the profile, an end conduit25 at the free end of the horizontal flank of the second profile elementand at the free end of the lower portion 18 of the first profile element10, which end conduit has a cross-section resembling a portion of acircular arc. Adjacent extension joint structures are interconnected attheir ends by means of spring pins placed at the end conduits, or usingshort bars (not shown) fitted in the end conduits so that the barsextend across the joining point and prevent the ends of the expansionjoint structures from moving in relation to each other. The end conduitsalso enhance the bonding of the profile elements to the concrete. Tofurther enhance the bonding, the profile element surfaces intended to bein contact with the concrete may be roughened.

[0022] In an expansion joint structure according to the invention theprofile elements 10, 12 and the connecting strips 28 constitute a singleextruded aluminum profile. The connecting strips are attached to theprofile elements through very thin necks which keep the elementstogether during the casting of the slab. The necks-are so thin that theycan be broken by hand. Thus the connecting strips can be detached fromthe profile elements simply by tearing them off by hand when theconcrete has hardened enough. Expansion joint structures can bemanufactured in different sizes for different uses and environments.Advantageously the overall height of an expansion joint structure isabout 10 to 15 cm. The thickness of a profile element wall isadvantageously about 2 to 3 mm. The length of an expansion jointstructure can be chosen on the basis of manufacturing, transport, andinstallation criteria, for example. Advantageously the length of anexpansion joint structure is 3 to 5 meters. During installation, theprofile elements are kept together by the connecting strips 28. At thesame time the connecting strips prevent fresh concrete from entering thegap 26, thus keeping the gap clean during the casting phase. As soon asthe concrete surface has been leveled and floated, the connecting stripsare torn off the profile elements so that deformations caused by thecontraction of the slab can occur freely. After that, an elastic sealant72 (FIG. 3) is installed in the gap. Optionally, after removing theconnecting strips a temporary removable protecting band can be installedin the gap for the duration of the drying of the slab, in which case thesealant 72 proper is installed later when the concrete has hardenedenough.

[0023]FIG. 2 shows, by way of example, an expansion joint structure 1according to the invention cast-in in a concrete slab system. FIG. 2depicts the situation immediately after the casting of the slab.Installation of the expansion joint structure is begun by driving intothe concreting base 62 mounting rods 50, each of which has one endsharp, in an upright position, advantageously at about one-meterintervals. The mounting rods 50 are advantageously about 40-cm-long bitsof ordinary 10-mm corrugated steel rod. The mounting rods are aligned ina straight line at the expansion joint with the help of an alignmentwire, and their top ends are positioned at the exact height specified,advantageously using a leveling instrument or laser beam. The expansionjoint structure is then mounted on the mounting rods such that the endsof the mounting rods go into the channel 40 between the profileelements, and the edges of the ledges 30, 32 rest on the ends of therods. An alternative advantageous method of supporting the expansionjoint structure is to cast small concrete legs at about one-meterintervals along the joint with the help of an alignment wire. Afterthat, the expansion joint structure is aligned on top of the concretelegs and adjusted at the exact specified height using a laser beam, forexample. The slab proper is cast when the concrete legs have hardenedenough, i.e. the next day in most cases.

[0024] The upper edge of the expansion joint structure is fixed prior tothe casting of the slab proper, in one of the ways discussed above, asprecisely as possible to the height corresponding to the upper surfaceof the slab to be poured so that the expansion joint structure can beutilized e.g. as a screed mark in the leveling of the slab surface whenthe slab is poured. If the gap between the concreting base 62 and thelower edge of the expansion joint structure 1 is large, it can becovered with a separate boardlike barrier 71 advantageously screwed orriveted onto the lower portion 18 of the first profile element.

[0025] A concrete slab is cast, depending on the size of the slab andother factors, either in one pour or in several pours. If the slab issmall, the concrete slabs 66 a, 66 b on both sides of the expansionjoint structure can be cast in one pour. Large slabs usually cannot becast in one pour, but the concreting has to be done over a span ofseveral days. In such a case the concreting can be interrupted at theexpansion joint, and pouring can be continued the following day. Theexpansion joint structure serves then also as a construction joint form.As the concrete hardens, the expansion joint structure becomes part ofthe concrete slab. The trapezoid shape of the first profile element 10causes a wedge-like concrete dowel to be formed in the joint between theconcrete slabs 66 a, 66 b which concrete dowel receives shear stressespresent at the joint. In order to enhance the bondage of the profileelements to the concrete cast, bondage strips 54 are attached to theprofile elements at the installation phase of the joint structure. Thebondage strips are V-shaped aluminum strips attached, advantageously bymeans of welding, by their ends to a surface of a profile element.Naturally, other kinds of bondage elements may be used as well, such ase.g. threaded bars attached by a bolt to a hole drilled through the wallof a profile element.

[0026]FIG. 3 shows, by way of example, a cross section of an expansionjoint structure 1 according to the invention cast-in in a concrete slab.FIG. 3 depicts a situation where the slab is at least partly set andcontraction in the slab has begun. When extra water exits, the slabs 66a, 66 b contract. The slab edges will then withdraw towards theirrespective contraction centers, leaving a gap between the slabs. Whenusing, an expansion joint structure according to the invention, thefirst profile element 10 will bond to the first concrete slab 66 a, andthe second profile element 12 to the second concrete slab 66 b, wherebydeformations caused by slab contraction will primarily occur at the gap26. In order to allow deformations caused by contraction to occurfreely, the connecting strips 28 should be removed as soon as possible,advantageously immediately after the floating. After that, the gap 26 isfilled with elastic sealant 72 which will conform to the movements ofthe slab edges. The sealing strips protected the gap during the pouringwork so that the sealant will readily adhere to the clean walls of thegap. The expansion joint will thus be watertight. As the concreteshrinks, the end surface of the second slab 66 b will come off the firstprofile element 10 and barrier 71, thus resulting in a tongue-and-groovestructure at the slab joint which will transfer shear stresses.

[0027] Above we described a few advantageous embodiments of an expansionjoint structure according to the invention. The invention is not limitedto the solutions described above, but the inventional idea can beapplied in numerous ways within the scope defined by the claims attachedhereto.

1. An expansion joint structure (1) for concrete slabs, comprising a first profile element (10) to be attached to an edge of a first concrete slab (66 a), and a second profile element (12) to be attached to an edge of a second, adjacent, concrete slab (66 b), said profile elements being joined together by at least one removable connecting strip (28) such that there is a gap (26) between the profile elements, characterized in that the first profile element and second profile element and the connecting strips form a single continuous aluminum profile.
 2. An expansion joint structure according to claim 1, characterized in that the connecting strips (28) are attached by a first edge to the first profile element (10) and by a second edge to the second profile element (12) through thin necks such that they can be torn off.
 3. An expansion joint structure according to claim 1 or 2, characterized in that there are two connecting strips (28) and the first connecting strip is placed at the upper edge of the gap (26) and the second connecting strip is placed at the middle or lower portion of the gap.
 4. An expansion joint structure according to any one of claims 1 to 3, characterized in that the width of the gap (26) between the first and second profile elements (10, 12) is about 10 millimeters.
 5. An expansion joint structure according to any one of claims 1 to 4, characterized in that the first profile element (10) and/or second profile element (12) comprise means (25) for coupling expansion joint structures together.
 6. An expansion joint structure according to any one of claims 1 to 5, characterized in that the first profile element (10) is designed such that it serves as a concreting form or construction joint form.
 7. An expansion joint structure according to claim 6, characterized in that the cross section of the first profile element (10) is shaped such that it provides an expansion joint form which can transfer shear stresses.
 8. An expansion joint structure according to any one of claims 1 to 7, characterized in that the first profile element (10) and/or second profile element (12) comprise bondage elements (54) in order to enhance the bonding of the profile elements to the concrete slabs (66 a, 66 b).
 9. An expansion joint structure according to any one of claims 1 to 8, characterized in that a sealant (72) is to be inserted in the gap (26) after removing the connecting strips (28). 